Replace object's normals with normal map
this can be eliminated in two ways the simplest and immediate is to set, the angle of smooth to 30 degrees,


or second way is to determine which edges should be planar, but this requires a selection of all edges of planar faces by setting the sharp edges, and adding a layer of custom normal edge.


However, I suggest you also take a look at the manual, where you can better understand these commands.
https://docs.blender.org/manual/en/dev/modeling/meshes/editing/smoothing.html